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J. Biol. Chem., Vol. 281, Issue 6, 3227-3236, February 10, 2006

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TRP Channels Are Inhibited by cAMP and Contribute to Pacemaking in Neurosecretory Insect Neurons^*

Dieter Wicher¹, Hans-Jürgen Agricola, Roland Schönherr^¶, Stefan H. Heinemann^¶, and Christian Derst^||

From the Department of Neurohormones, Saxon Academy of Sciences, 07743 Jena, Germany, the Institute of Zoology, Friedrich Schiller University, Jena, Germany, the ^¶Institute of Molecular Cell Biology, Friedrich Schiller University, Jena, Germany, and the ^||Center for Anatomy, Charité, Berlin, Germany

From a neuronal cDNA library of the cockroach Periplaneta americana we isolated a 3585-bp cDNA sequence encoding Periplaneta transient receptor potential (pTRP), a protein of 1194 amino acids showing 65% identity to the orthologous Drosophila channel protein dTRP. Heterologous expression of pTRP in HEK293 cells produced a constitutively active, non-selective cation channel with a Ca²⁺:Na⁺ permeability ratio of 2. In contrast to dTRP-mediated currents, pTRP currents were partially inhibited by 8-bromo-cAMP, and this effect was not mediated by protein kinase A (PKA) activation. pTRPb, a truncated pTRP splice variant missing most of the C terminus, was insensitive to 8-bromo-cAMP. Thus, the critical cAMP-binding site seems to be located in the C-terminal part of pTRP, although there is no common cAMP-binding consensus sequence. While dTRP is only expressed in the photoreceptors, pTRP is expressed throughout the nervous system. In particular it is expressed in dorsal unpaired median (DUM) neurons. In these octopamine-releasing, neurosecretory cells a Ca²⁺ background current contributing to pacemaker activity was found to be up-regulated by the reduction of cAMP level. In addition, the Ca²⁺ background current was inhibited by LOE-908, 2-APB, and La³⁺, which similarly affected the pTRP current. We thus propose that the pTRP protein is involved in forming the channel passing the Ca²⁺ pakemaking background current in DUM neurons.

Received for publication, October 31, 2005 , and in revised form, November 22, 2005.

^* This work was supported in part by Deutsche Forschungsgemeinschaft Grant Wi 1422/2-4,5. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, D-07745 Jena, Germany. Tel.: 49-3641-949360; Fax: 49-3641-571002; E-mail: dwicher{at}ice.mpg.de.

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